When a sheet metal is press-formed, problems such as a decrease in shape fixability due to a warp (spring back) of a press-formed part or angular variation occur.
In order to decrease the spring back and improve dimensional accuracy of the press-formed part, it is generally known that increasing a blank holding force is effective at the last period of press-forming.
In Patent Document 1, a technology is suggested in which an elastic body such as a spring is disposed in a die member included in a press-forming die and thus, a blank holding force is increased in the last period of press-forming.
In Patent Document 2, a technology is suggested in which a coned disc spring capable of generating a high load even at a low stroke is provided as the spring disposed in the die member included in the press-forming die and thus, a blank holding force which is increased in the last period of press-forming is higher.